Improvement of Electrochemical Water Oxidation by Fine-Tuning the Structure of Tetradentate N4 Ligands of Molecular Copper Catalysts

• Two copper complexes, [(L1)Cu(OH2)](BF4)2 [1; L1=N,N′-dimethyl-N,N′-bis(pyridin-2-ylmethyl)-1,2-diaminoethane] and [(L2)Cu(OH2)](BF4)2 [2, L2=2,7-bis(2-pyridyl)-3,6-diaza-2,6-octadiene], were prepared as molecular water oxidation catalysts. Complex 1 displayed an overpotential (η) of 1.07 V at 1 mA cm−2 and an observed rate constant (kobs) of 13.5 s−1 at η 1.0 V in pH 9.0 phosphate buffer solution, whereas 2 exhibited a significantly smaller η (0.70 V) to reach 1 mA cm−2 and a higher kobs (50.4 s−1) than 1 under identical test conditions. Additionally, 2 displayed better stability than 1 in controlled potential electrolysis experiments with a faradaic efficiency of 94 % for O2 evolution at 1.58 V, when a casing tube was used for the Pt cathode. A possible mechanism for 1- and 2-catalyzed O2 evolution reactions is discussed based on the experimental evidence. These comparative results indicate that fine-tuning the structures of tetradentate N4 ligands can bring about significant change in the performance of copper complexes for electrochemical water oxidation.

Ämnesord

NATURVETENSKAP  -- Kemi -- Annan kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Other Chemistry Topics (hsv//eng)

Nyckelord

copper

electrocatalysis

homogeneous catalysis

N ligands

water oxidation

Catalysis

Catalysts

Ligands

Oxidation

Rate constants

Controlled potential electrolysis

Experimental evidence

Faradaic efficiencies

Phosphate buffer solutions

Possible mechanisms

Tuning

coordination compound

ligand

oxygen

water

chemical structure

chemistry

electrochemical analysis

electrolysis

oxidation reduction reaction

procedures

Coordination Complexes

Electrochemical Techniques

Molecular Structure

Oxidation-Reduction

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